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Zeiss 15/2.8 Distagon Q&A — Testing

ZF.2 15mm f/2.8 Distagon T*

This is one of several pages resulting from the March 13, 2012 discussion with Staff Scientist Dr. Hubert Nasse. See the original list of questions.

These pages are a summary of the discussion based on notes taken, and as reviewed by Dr. Nasse. Bracketed comments [ ] are editorial in nature.

ZEISS maintains rigorous quality standards for durability across extreme usage conditions:

  • Storage at high and low temperatures (55°C , -40°C).
  • Rapid temperature changes.
  • Damp heat.
  • Vibration and shock in various directions.
  • See the YouTube video: youtu.be/LVssYtOJP2U.

When a design is finalized, a first batch of a dozen lenses is made and they are all tested extensively. This process can take an entire week.

After the initial dozen lenses are tested and the results are analyzed, 40 production samples are made (possibly with modifications to address any issues), then these are also tested similarly. If all goes well, then production starts.

Each lens is MTF tested and actual performance is compared to theoretical performance before and after each testing challenge.

Environmental testing

A “torture chamber” of heat/cold over 24 hours is used to test the lens integrity over extreme conditions. This testing has its roots in military applications, e.g., submarine and tank optics.

ZEISS lenses are metal. Some (other brand) plastic lenses cannot hold up to such conditions, and since plastic deforms, such lenses when tested can be irreversibly damaged (think “hot car”).

[50°C 122°F is less than the ambient air temperature in Death Valley on a hot summer day, let alone a hot car! I have personally visited in July and seen readings of 125° F, the record is 134°F, and ground temps can reach 201°F. What happens to plastic gear on such a day?]

Vibration and shock tests

Vibration can be a real danger for screws. The vibration and shock tests are much less friendly than most users are likely to experience, but ZEISS does not recommend tossing their lenses into the bed of a pickup truck, then letting them roll around over 50 miles of dirt roads.

Sometimes prototypes exhibit issues, these issues are addressed, then new prototypes retested before production begins.

Most shocks/bangs are not worth worrying about, for example, the camera around the neck bangs into the wall— this should be well below the level at which any shock damage could occur.

Even after years of use, the expectations remain high for a lens continuing to offer the same optical performance. ZEISS retests lenses after some years of use to gain insight into possible

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